Self destructing pesticidal formulations and methods for their use

ABSTRACT

NORMALLY PERSISTENT PESTICIDES SUCH AS DDT ARE FORMULATED AS SMALL PARTICLES WITH A REACTIVE METAL OR METALLIC COUPLE AND AN ACID-PRODUCING AGENT. MEANS ARE PROVIDED TO MAINTAIN THE PESTICIDE IN ISOLATION FROM THE REACTANTS FOR A PREDETERMINED LENGTH OF TIME AFTER FIELD APPLICATION. THEREAFTER, THE REACTANTS ARE ALLOWED TO CONTACT THE PESTICIDE RESULTING IN ITS DEGRADATION TO LESS HARMFUL COMPOUNDS.

Oct. 23, 1973 K. H. SWEENY ET AL 3,767,783

SELF-DESTRUCTING PESTICIDAL FORMULATIONS AND METHODS FOR THEIR USE Filed Dec. 23, 1970 KEITH H. SWEENEY JAMES R. FISCHER CHARLES A. LU/VG ELMER M WILSON BY BM MAM ATTORNEYS United States Patent "ice 3,767,783 SELF-DESTRUCTING PESTICIDAL FORMULA- TIONS AND METHODS FOR THEIR USE Keith H. Sweeny, West Covina, James R. Fischer, Claremont, Charles A. Lung, Buena Park, and Elmer M. Wilson, Pasadena, Calif., assignors to the United States of America as represented by the Secretary of the Interior Filed Dec. 23, 1970, Ser. No. 100,985 Int. Cl. A611: 9/00 U.S. Cl. 4242 8 Claims ABSTRACT OF THE DISCLOSURE Normally persistent pesticides such as DDT are formulated as small particles with a reactive metal or metallic couple and an acid-producing agent. Means are provided to maintain the pesticide in isolation from the reactants for a predetermined length of time after field application. Thereafter, the reactants are allowed to contact the pesticide resulting in its degradation to less harmful compounds.

BACKGROUND OF THE INVENTION A number of extremely useful pesticides also possess great stability and show little degradation when exposed to ordinary environmental conditions. Hence, they persist in soil and water for long periods of time; often for many years. Repeated use of such pesticides may even result in a continuing build-up of residual pesticide concentration in the environment.

Such environmental stability is a very desirable characteristic for some uses as in long term termite protection of buildings and other structures. That same characteristic is undesirable when the pesticide is used for the short term control or eradication of a particular organism. Typical of such useful but persistent pesticides are the halogenated organics exemplified by DDT, chlordane, toxaphene, dieldrin and the like.

It is now recognized that at least some of these pesticides are retained within the body of many organisms and higher animals resulting in progressively higher concentrations of pesticide as one progresses up the food chain. It has also been recognized that relatively high concentrations of pesticide will affect metabolic processes, particularly reproductive functioning, of some animals. For example, DDT has been linked to the so-called soft shell syndrome observed in a variety of birds.

In spite of their ecological hazards, no really satisfactory substitute is available for many of the halogenated hydrocarbons in a number of specific uses. Many of the undesirable side effects of halogenated organic pesticides would be alleviated if they were less stable and degraded to form innocuous products after a relatively short exposure to environmental conditions.

SUMMARY OF THE INVENTION We have found that stable pesticide compounds, such as halogenated organics, may be formulated to obtain their complete or nearly complete destruction within a predetermined time after field application. The formulation includes an integrated, self-destructing pesticide particle comprising the pesticide, a material which reacts with the pesticide, and a means to delay the reaction for a predetermined length of time.

A specific embodiment of our invention comprises a formulation of a halogenated organic pesticide such as DDT with a reductant such as a zinc-copper couple in combination with a material which supplies a localized acidic environment. The pesticide is segregated from the reductant by a coat ng material which disintegrates within 3,767,783 Patented Oct. 23, 1973 a predetermined period of time after field application thus giving a reaction delay.

OBJECTS OF THE INVENTION It is an object of our invention to provide a particulate, self-destructing pesticide formulation.

Another object of our invention is to provide a method for the application of normally persistent pesticides to a field environment while avoiding residual accumulations of those materials.

Yet another object of our invention is to provide a process for the formulation of self-destructing pesticide particles.

DETAILED DESCRIPTION OF THE INVENTION The invention will be more clearly understood by reference to the accompanying drawings in which:

FIG. 1 represents a generalized cross-sectional view of a self-destructing pesticide particle.

FIG. 2 is a cross-sectional representation of another embodiment of our pesticide formulation.

Referring now to FIG. 1, an individual formulated pesticide particle is generally represented by the numeral 10. The particle comprises a central core 11 of a reactant material which is preferably a metal or a metallic couple capable of either reducing or polymerizing the pesticide to biologically inactive forms. Coated on the core preferably as a continuous layer, is solid, acid-producing material 12. Layer 13 comprises a relatively thin, continuous coating which serves to temporarily isolate the reactive inner portion of the particle from the environment. Preferably layer 13 comprises a film-forming material which decomposes or dissolves within a relatively short but predictable period after being exposed to a typical outdoor environment. Finally, exterior layer 14 comprises a pesticidal composition adhering to coating 13.

Size of the composite particles is preferably within the range of conventional pesticidal powders adapted for application by air dispersion. Diameter of the individual composition particles should be within the general range of about 1 to about microns. The optimal and preferred particle size to achieve highly eflicient pest control action and uniformity of application ranges from about 5 to about 20 microns.

In co-pending commonly assigned patent applications Ser. Nos. 100,975 and 101,201, now U.S. Pat. No. 3,640,- 821, there is disclosed the reaction of DDT and other chlorinated organic pesticides with metallic zinc and a variety of metallic couples in an acid environment to produce relatively innocuous degradation products. Any of the metal reductants disclosed in those applications may be used as the reactive central core material 11. These metal reductants include metallic zinc and metallic couples comprising a minor amount of a catalytic metal, such as copper or silver, combined with a major amount of a reductant metal such as zinc, aluminum, iron, cadmium and magnesium. Examples of metallic couples useful in our invention include zinc-copper, zinc-silver, alu minum-copper, iron-copper, magnesium-copper and cadmium-copper. Of these metallic reductants, the following are preferred: metallic zinc, zinc-copper, aluminum-copper and iron-copper.

It is preferred that the metallic reductant be present in stoichiometric excess relative to the pesticide. In the degradative reaction of metallic zinc or zinc couple with p,p'-DDT, for example, the reaction proceeds via chlorine removal to form relatively non-toxic products. The major end product of this reaction is l,1-bis(p-chlorophenyl) ethane which theoretically requires 3 equivalents of reductant per mol of DDT. On a weight basis, 0.28 lb. of zinc is required to reduct 1 lb. of DDT. However, it is preferred that zinc be present in about 2 to 10 times the stoichiometric requirements. An equal weight of zinc and DDT, representing a stoichiometric excess of a factor of about 4, has given good results.

When using aluminum-copper or iron-copper couples, there occurs a different type of reaction with DDT. In these cases, the DDT is essentially dimeri'zed to form a compound which has been identified as 1,l,4,4-tetra (pchlorophenyl)-2,2,3,3-tetrachlorobutane. This compound is lipoid insoluble and appears to exhibit little if any physiological activity. Only one equivalent of reductant is required per mol of DDT in the reaction. Hence, only 0.025 lb. of aluminum or 0.052 lb. of iron is theoretically required per lb. of DDT. Again, it is preferred that the metal be present in about 2 to times that amount theoretically required.

The metallic couples may be prepared in a variety of simple ways. For example, preparation of a metal-copper couple may be carried out by contacting a metal powder with a dilute solution of a copper salt such as the sulfate or chloride. A thin film of metallic copper is thus deposited over the surface of the metal particles. Generally, about 0.1 to about 10 milliequivalents of copper are used per gram of metal powder. Optimum results were achieved at a copper level of about 1 meq. per g. of metal particles. Other methods of preparation, such as by the hot reduction of a mixture of metal and cupric oxide to yield a metal alloy, gave substantially equivalent results.

Acid producing material 12 may comprise any of a large variety of solid acids or hydrolyzable salts. Any such compound which can produce a localized acidic environment having a pH below about 4, and preferably on the order of pH 2, may find use in our pesticidal composition provided further that it can be deposited as a layered coating around a metal particle. Examples of solid acids which may be used include a number of the lower, solid monocarboxylic acids, dicarboxylic acids such as oxalic and malonic; tricarboxylic acids such as citric; halogen substituted organic acids such as chloroacetic and such miscellaneous acids as sulfamic. Metal salts, particularly those of aluminum and ferric iron, which hydrolyze to form an acidic environment, may also be used. In a preferred embodiment, there is incorporated with the acid producing material an emulsifying agent for the pesticide. Examples of emulsifying agents which may be used include surfactants such as those based on alkyl-aryl polyether alcohols, sulfonates and sulfates.

The amount or proportion of acid producing material incorporated within each particle is not critical. It is necessary that material 12 maintain a localized acidic environment for a period of time of at least about an hour and preferably for a time period of several hours to several days after disintegration of the particle is initiated.

Coating layer 13 serves to temporarily isolate the pesticide from the reactive central particle core. It is composed of a material which degrades, decomposes or dissolves upon exposure to an ordinary field environment .for a pre determined length of time. Coating 13 may comprise a material which slowly dissolves upon exposure to a damp or wet environment or which decomposes upon exposure to ultraviolet radiation or even to oxygen. Examples of appropriate coating materials include trimethyl silyl compounds, microcrystalline waxes, modified polyvinyl alcohols, polyesters, polyethylene and a variety of condensation polymers.

Coating layer 13 may be applied using a number of conventional techniques. For example, the coating material may be dissolved in a suitable solvent and slurried with the particle. After driving off the solvent, usually by heating, the individual particles retain a thin layer of the coating material. Depending upon the coating material, other techniques may be used including vapor deposition, fluidized bed coating processes and precipitation of coating materials from solution.

Exterior layer 14 comprises a pesticide preferably applied in an adhering but discontinuous fashion to coating layer 13. The pesticide may comprise any one or a mixture of halogenated organic compounds. These compounds include DDT, toxaphene, lindane, methoxychlor, dieldrin, Kelthane, chlordane, Perthane, endrin, aldrin, heptachlor and the like. Kelthane is a trademark for an agricultural miticide based on l,l-bis(para-chlorophenyl)-2,2,2-trichloroethanol while Perthane is a trademark for an agricultural insecticide based on I,l-dichloro-2,2-bis(paraethylphenyl)ethane. Since the bulk of the pesticide is exposed to the environment in this arrangement, there is little if any reduction in pesticidal activity compared with normal formulations.

Field life of the pesticidal composition may be varied in several ways. First, by proper selection of the material making up isolating coating layer 13, it is possible to adjust average field life over a wide time range. Secondly, by varying the thickness of layer 13, average field life may be varied over a somewhat shorter time span.

FIG. 2 illustrates another embodiment of our pesticidal formulation. Numeral 20 generally represents a crosssectional view of a single composite particle having a reactive central core 21, an acid-producing layer 22 and an environmental isolation layer 23. Dispersed upon and adhering to layer 23 are a plurality of pesticide particles 24 exposed and available for pest control action. Composition of each of the layers making up composite particle 20 is similar to the corresponding layer of particle 10.

Tests with a Greenfield sandy loam soil, considered to be representative of many California agricultural regions, were used to evaluate other techniques for the controlled decomposition of DDT. In one series of tests, DDT was sprayed as an emulsifiable concentrate onto soil flats at the rate of 1 lb. DDT per acre. Particles of zinc-copper couple having a nominal particle size of about 5 microns were then sprayed onto the same soil flats followed by a dilute acetic acid spray. The samples were exposed to an out-ofdoors environment for 4 days and were then extracted and analyzed. It was found that about 40 to 45% of the DDT had decomposed during this time but that only a trace of the preferred degradation product DDEt (1,1-bis(p-chlorophenyl)-l,l-chloroethane) had been formed. On the other hand, when a composite particle formulation comprising DDT and the zinc-copper couple, were applied to the soil under the same or similar conditions, about of the DDT decomposed within 4 days giving DDEt as the major decomposition product.

What is claimed is:

1. A particulate composite pesticidal composition comprising:

a pesticide chosen from the group consisting of DDT, toxaphene, lindane, methoxychlor, dieldrin, Kelthane, chlordane, Perthane, endrin, aldrin and heptachlor;

a metallic reductant chosen from the group consisting of metallic zinc and the metallic couples of zinccopper, zinc-silver, aluminum-copper, iron-copper, magnesium-copper and cadmium-copper;

an acid producing material chosen from the group consisting of solid acids and the hydrolyzable inorganic salts of aluminum and ferric iron, and

means defining an exterior surface deposit of said pesticide adhered to a layer of a material which degrades after exposure to a field environment for a predetermined iength of time, said material chosen from the group consisting of trimethyl silyl compounds, microcrystalline waxes, modified polyvinyl alcohols, polyesters, polyethylene and condensation polymers formed around a layer of said acid-producing material formed upon a central core of said metallic reductant, said means thereby isolating the pesticide from the metallic reductant for a predetermined length of time after exposure of the composition to a field environment.

2. The composition of claim 1 wherein the mean diameter of the composite particles is in the range of about 5 to 20 mic ons.

3. The composition of claim 2 wherein the pesticide is DDT and wherein the reductant is chosen from the metallic couples of zinc-copper, iron-copper and aluminum-copper, said metallic couple being present in 2 to fold excess over that stoichiometrically required to completely react with the DDT.

4. The composition of claim 3 wherein a DDT emulsifying agent is incorporated with the acid producing material.

5. The composition of claim 4 wherein the coating layer isolating pesticide from reductant is chosen from the group consisting of trimethyl silyl compounds, microcrystalline waxes and polyvinyl alcohols which degrade, decompose or dissolve after exposure to ultraviolet radiation, oxygen or water of a damp or wet field environment for a predetermined length of time.

6. A process for decreasing the residual concentration of a normally persistent pesticide which comprises applying a pesticide chosen from the group consisting of DDT, toxaphene, lindane, methoxychlor, dieldrin, Kelthane, chlordane, Perthane, endrin, aldrin and heptachlor to a field environment as a formulation having self-destructing properties, said formulation comprising a composite of the pesticide with a material normally reactive with the pesticide to produce environmentally innocuous degradation products, said material normally reactive with the pesticide being chosen from the group consisting of metallic zinc and the metallic couples of zinc-copper, zinc-silver, aluminum-copper, iron-copper, magnesium-copper and cadmium-copper;

maintaining the pesticide in isolation from the reactive material for a predetermined time by the defined means of the composite pesticide composition of claim 1 and thereafter allowing the pesticide to interact with the reactive material.

7. The process of claim 6 wherein the .formulation includes an acid producing material capable of producing a localized acidic environment having a pH below about 4 during the reaction of the pesticide with the metallic material.

8. The process of claim 7 wherein the pesticide is DDT and wherein the metallic material is present in amounts in excess of that required to stoichiometrically react with the DDT.

References Cited UNITED STATES PATENTS 3,206,297 9/1965 OConnor 7l28 2,069,710 2/ 1937 Missbach 424162 X 1,911,868 5/1933 Young 424162 X 2,165,206 7/1939 Bacon et al. 424-162 X 2,414,193 1/1947 Durham 424354 X 2,786,012 3/1957 McHan 424357 X 2,547,261 4/ 1951 Geiger et a1. 424164 X 2,491,632 12/1949 Wieder 424164 2,414,216 1/1947 Wean et al 424354 X 2,461,852 2/1949 Stein et al. 260-649 3,640,821 2/1972 Sweeny et al. 210-59 FOREIGN PATENTS 1,945,108 3/ 1970 Germany.

571,484 8/ 1945 Great Britain. 1,300,133 7/ 1969 Germany.

624,136 5/ 1949 Great Britain.

OTHER REFERENCES Fleck et al., Ind. & Eng. Chem. 37 (4): 403-405, April 1945, Compatibility of DDT With Insecticides, Fungicides and Fertilizers.

Fleck et al., J.A.C.S. 66: 2095, December 1944, Catalytic Removal of Hydrogen Chloride From Some Substituted a-Trichloroethanes.

Gunther et al., Science 104: 203-204, August 1946, Inhibition of the Catalyzed Thermal Decomposition of DDT.

C.A. 43 #199b, #3697d (1949), C.A. 46, #6787h, #7274b (1952), C.A. 48, #315g (1954), C.A. 59, #9259h (1963): Birrell, Thermal Decomposition of DDT by Some Soil Constituents.

SHEP K. ROSE, Primary Examiner U.S. Cl. X.R. 

